The present invention relates to the field of mass-storage devices. More particularly, this invention relates to a method and apparatus for isolating actuator noise from disc drives.
Devices that store data are key components of any computer system. Computer systems have many different devices where data can be stored. One common device for storing massive amounts of computer data is a disc drive. The basic parts of a disc drive are a disc assembly having at least one disc that is rotated, an actuator that moves a transducer to various locations over the rotating disc, and circuitry that is used to write and/or read data to and from the disc via the transducer. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved from and written to the disc surface. A microprocessor controls most of the operations of the disc drive, in addition to passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The disc drive includes a transducer head for writing data onto circular or spiral tracks in a magnetic layer the disc surfaces and for reading the data from the magnetic layer. In some drives, the transducer includes an electrically driven coil (or xe2x80x9cwrite headxe2x80x9d) that provides a magnetic field for writing data, and a magneto-resistive (MR) element (or xe2x80x9cread headxe2x80x9d) that detects changes in the magnetic field along the tracks for reading data.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area. The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particular desired fly height. The fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film greatly reduces the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation. In some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc-drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc. Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track. The data is divided or grouped together on the tracks. In some disc drives, the tracks are a multiplicity of concentric circular tracks. In other disc drives, a continuous spiral is one track on one side of a disc drive. Servo feedback information is used to accurately locate the transducer. The actuator assembly is moved to the required position and held very accurately during a read or write operation using the servo information.
When the disc assembly is rotated at high speed, the air adjacent to the spinning disc or discs is caused to move as well. This moving air moves between the rotating disc and the read/write transducer, creating an air bearing, and advantageously causing the transducer to xe2x80x9cflyxe2x80x9d over the disc surface.
The impact of high acoustic emissions from disc drives is well known in the art. High acoustic intensities and/or emission result in a less comfortable computing environment, and generally cause acoustic noise. Government agencies throughout the world are now requiring that the decibel level of average sound energy emanating from office equipment be substantially reduced. Computer manufacturers are also placing acoustic emission standards on disc drive manufacturers. Manufacturers of disc drives have also long recognized that certain improvements for data storage performance in disc drives, namely, to increase disc rotation velocity and to increase head actuator movement frequency, contribute to unwanted acoustic noise.
Several methods to reduce the intensity of unwanted acoustic noise have been attempted. Among the several methods are the use of external dampening techniques for the entire disc drive. For example, mechanically isolating the cover of a disc drive from the mechanical reinforcement structure with a continuous airspace. Many designers believe that most of the unwanted acoustic frequencies emanate from a xe2x80x9cdrum-likexe2x80x9d top cover and from the base plate of the disc drive. Some designers have made strides in addressing the acoustic frequencies that escape from the top cover. The designers use cover dampeners and adhesives with inherent dampening properties on the cover. Other designers have attempted to isolate the transducer actuator in order to reduce the unwanted acoustic emissions at multiple frequencies. Such actuator isolation conventionally includes using plastic and rubber mounts on the pivot bearing assembly of the actuator. Many environments where disc drives are used are sensitive to the amount of acoustic emissions (or noise) coming from an operating disc drive. Therefore, it is desirable to reduce such acoustic noise.
Acoustic emissions are higher and more prevalent during rapid data access and storage operations, and in particular during xe2x80x9cdisc seek operations,xe2x80x9d or simply xe2x80x9cseeks.xe2x80x9d A xe2x80x9cseekxe2x80x9d is movement of an actuator assembly from a first track to a second target track. Many attempts have been made to lower acoustic emissions during disc seeks. Previous attempts have either centered on dampening the acoustic energy already in a disc base plate by placing foam between a printed circuit board and the base plate, or on decoupling the spindle and actuator mechanism from its enclosure by using a plurality of rubber isolator mounts. Other attempts include moving the actuator with less force to reduce impulse forces and thus reduce large acoustic spikes. Nevertheless, each of these improvements have proved marginal, and some have been prohibitively costly. What is needed is a method and apparatus to substantially reduce unwanted acoustic emissions at or near the actuator. Also needed is an inexpensive method and apparatus.
A method and apparatus is described for isolating actuator noise in disc drives. An actuator isolator mount is provided in between the actuator and the base plate of the disc assembly. A disc drive includes an actuator assembly on a rotational axis, a base plate, and a dampening member for reducing acoustic noise from traveling in an axial direction in the actuator assembly. The dampening member is positioned between the actuator assembly and the base plate.
In some embodiments, the dampening member includes an energy absorbing material positioned to dampen vibrations substantially parallel to a rotational axis of the actuator assembly, and to dampen vibrations transverse to the rotational axis of the actuator assembly. The dampening member also may include a rigid dampening mount. The base plate of the disc drive may also have a stepped mounting surface and a shoulder for the dampening member. When the base plate includes a mounting surface for the actuator assembly, the dampening member is positioned substantially flush to the surface of the base plate within a counter bore therein, sized to receive the dampening member.
The dampening member may be cylindrical or may be a sleeve of elastomeric material fitting around a cylinder. The dampening member may also have a cylinder adjacent to a circular end of the cylinder and/or a through-opening. The dampening member reduces the acoustic noise on at least two axes. The dampener reduces acoustic noise due to a lateral vibration and a radial vibration.
Another aspect of the present invention provides a method for substantially reducing vibrations of the actuator assembly. Vibrations from the actuator assembly are reduced or prevented from entering a base plate of a disc drive. The method includes the steps of isolating vibrations that are substantially parallel to the rotational axis of the actuator assembly, and isolating vibrations that are transverse to the rotational axis of the actuator assembly. The isolating step includes mounting a dampening member to the base plate of a disc drive. Mounting the dampening member includes affixing a metal plug within a cavity in the base plate, holding the metal plug within the base plate to form a joint union, and inserting an elastomer in a fluid-state under atmospheric pressure in and around any space left between the joint union of the base plate and the metal plug. The elastomer seals the joint union.
The joint union of the base plate, the elastomer, and the metal plug are also cured. Curing yields the advantageous acoustic absorption properties.
A method for reducing ambient disc drive acoustic emissions includes forming a recessed cavity within a base plate, integrating a polymer dampening material with the base plate, forming the polymer in a shape to dampen acoustic noise, and attaching an actuator to the polymer. In one embodiment, integrating includes fabricating the base plate and the polymer as a unitary body using injection molding. Integrating the polymer to the base plate may also include fabricating the base plate and the polymer as a unitary body using transfer molding. An adhesive may also be used to integrate the polymer to the base plate. The adhesive used has substantial dampening properties.